U.S. patent application Ser. No. 08/805481, filed Feb. 25, 1997, now U.S. Pat. No. 5,690,173 assigned to the assignee of the subject patent application, describes a practice and apparatus for introducing gases into ground water to provide oxygen for the aerobic decomposition of organic contaminants. It is well known that naturally occurring micro-organisms resident in an underground formation can metabolize and thereby degrade organic material to carbon dioxide and water. While the organisms may be aerobic or anaerobic, the aerobic organisms are most effective in degrading gasoline and oil spills. Such micro-organisms can be employed to decompose an organic contaminant in a reasonable period of time provided that sufficient oxygen can be supplied to the working organisms.
The above patent application discloses the use of one or more wells drilled to a level below the table of the contaminated water. Where two wells are used, one well may be used as a recovery well and the other as an injection well. The recovery well is used to remove some of the contaminated water for analysis and/or treatment. Obviously, it is desirable to fully analyze samples withdrawn from a recovery well to ascertain the extent of the contamination and the progress achieved in its remediation. Such analysis enables a strategy to be developed to complete the remediation process. The existence of a recovery well also permits the use of groundwater treatment materials and devices above ground such as for the removal of chemical species that may plug the wells or otherwise interfere with the remediation treatment.
An injection well is used to return treated water and other materials to the contaminated subsurface formation. In accordance with the above-identified patent application, an injection well is also used to inject air or, preferably, oxygen into the water to support aerobic micro-organisms as they metabolize the organic contamination. In one form such an injection well included an outer pipe that was perforated, at least in the portion extending below the water table, and an inner pipe for introducing treated water, for example, back into the formation. Extending down from the surface and coiled around the inner or outer pipe was a polymeric hose for dispersing and dissolving molecular oxygen into the underground water. The hose was of suitable composition to hold oxygen gas under pressure and to permit the diffusion of oxygen molecules through the wall of the hose into the micro-organism bearing contaminated water and soil. By such means the oxygen was supplied slowly in amounts soluble in the water. Thus, the oxygen that was introduced into the formation could be dissolved in the groundwater to be utilized by the micro-organisms and not wasted by bubbling out of the region. Optionally, other nutrient gases may be supplied with the oxygen for remediation.
A suitable rubber or plastic hose, such as a silicone rubber hose, serves very well to oxygenate a contaminated region of anaerobic organisms. One end of the hose is closed. A high pressure source of oxygen is connected to the other end to deliver oxygen through the hose to the micro-organisms in the water or nearby soil. The combination of a recovery well and an injection well can be used to induce or assure a flow of water at a suitable rate past the oxygenation hose. The length of the coiled hose can be determined to provide enough diffusion area through the hose to provide a desired oxygen flow into the formation.
While the coiled diffusion hose works very well in many applications, there are applications where a simpler, lower maintenance, more versatile apparatus would be useful. It is an object of this invention to provide such a diffusion apparatus for bioremediation.